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Police: Bomb-making taught in Dagestan

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U.S. and Russian authorities interview Tamerlan and Dzhokhar Tsarnaev's parents

The two brothers are accused of staging deadly Boston Marathon bombings

The parents live in Dagestan, a part of Russia where Tamerlan visited

Tamerlan posted videos linked to jihadist militants after going to the region in 2012

The building, No. 50, that members of the Tsarnaev family call home sits on a seemingly quiet street in Makhachkala. The capital of Dagestan, a semi-autonomous republic in southern Russia, borders the Caspian Sea on one side and on the other overlooks the Caucasus Mountains.

For a time in 2012, Tamerlan Tsarnaev stayed here with his parents. He shopped at stores in Makhachkala, prayed at a local mosque.

What authorities want to know is whether it was here that Tamerlan learned, or perhaps was inspired, to kill.

The 26-year-old can't give an answer: He was killed after a shootout with U.S. authorities in Watertown, Massachusetts -- 5,500 miles from Makhachkala -- early Friday.

Days earlier, authorities say, he and his 19-year-old brother, Dzhokhar -- who is in a Boston hospital -- blew up two bombs at the finish line of the Boston Marathon. Three people died and scores were wounded in that attack.

FBI agents spent Wednesday in the Dagestani capital talking with Tamerlan and Dzhokhar's parents, according to an official in U.S. President Barack Obama's administration. The U.S. investigators were joined by members of Russia's Federal Security Service, human rights activist Kheda Saratova said.

Tamerlan Tsarnaev, one of the Boston Marathon bombing suspects, was the subject of an April 2009 photo essay that appeared in a graduate school magazine at Boston University. According to the article, he had hoped to become a naturalized American and make the U.S. Olympic boxing team. Authorities say an overnight shootout with police left him dead on April 19, 2013.

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Photos:Boston bombings suspect: Tamerlan Tsarnaev

Tsarnaev answers a call while walking to boxing practice at the Wai Kru Mixed Martial Arts center in Boston.

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Photos:Boston bombings suspect: Tamerlan Tsarnaev

Tsarnaev practices boxing at the Wai Kru Mixed Martial Arts center.

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Photos:Boston bombings suspect: Tamerlan Tsarnaev

Tsarnaev shows how he strengthens his ankles, according to the photo essay. The photographer did not want to be named for this story.

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Photos:Boston bombings suspect: Tamerlan Tsarnaev

Though he had lived in the United States for five years, Tsarnaev said in the essay: "I don't have a single American friend. I don't understand them."

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It's unclear what came of the parents' talk with U.S. and Russian authorities, though both parents had publicly insisted that their sons are innocent. But information has come out suggesting how Tamerlan Tsarnaev might have been influenced by his trip half a world from his Cambridge, Massachusetts, home.

While Dagestan may be picturesque in many respects, it's also been home to violence and civil unrest. That includes gun and bomb attacks targeting security services, including a suicide bombing at a police checkpoint that left 12 dead and dozens wounded while Tsarnaev was believed to be here.

After returning from his months-long visit to Russia, Tsarnaev created a YouTube channel that included two videos (since deleted) under a category labeled "Terrorists."

Analysis by CNN and the SITE Intelligence Group has uncovered a screen grab from one of those videos featuring members of Imarat Kavkaz, a potent militant Islamist group in the north Caucasus, which includes Chechnya and Dagestan.

Tsarnaev also appears to have posted and removed a video of a militant named Abu Dujan, a jihadist leader who was later killed by Russian troops.

Did Tsarnaev interact with Abu Dujan during his time in southern Russia? Authorities haven't publicly said anything on that point, either way.

Videos linked to his group show how to prepare homemade explosives from almost anywhere.

Askhabali Saurbekov, the police chief in the Dagestani town of Kizilyurt, said Abu Dujan met with foreigners before his death. This group included men, like Tsarnaev, who were of Chechen origin.